Laminated veneer lumber ("LVL") is a structural wood composite incorporating characteristics of both plywood and sawn lumber. Like plywood, LVL is made of adhesively bonded wood veneer sheets. But, whereas plywood is cross-banded, the veneer in LVL is bonded with the grain in most sheets running parallel, similar to sawn lumber. Because any veneer defects tend to be distributed evenly in LVL, dimensional flaws characteristic of sawn lumber are minimized, resulting in improved LVL structural properties.
In LVL manufacture, the ends of the individual veneer sheets are joined by either a lap, butt or scarf joint, with the joints being staggered throughout the cross-section of the LVL "billet". Glue is applied to the opposed, outer faces of each veneer sheet, excepting the two outermost planar surfaces. The glued sheets are laid atop one another to form the billet, which is then compressed and heated, firmly bonding the veneer into a single piece of LVL having superior strength characteristics. Veneer sheets of various dimensions can be used, including four foot by eight foot sheets; three foot by six foot sheets; or, eight foot by eight foot sheets. The billet may have any desired number of plys, with 7 to 35 plys being typical.
LVL may be made in a fixed length press or in a continuous layup press. In a fixed length press the entire billet fits between a pair of opposed platens which compress and heat the billet. In a continuous layup press an endless, continuously formed billet is slowly fed between the platens by a pair of steel belts which are rotatably driven around the respective platens.
A continuous layup press cures the billet as it is fed through the press. The feeding/curing process continues until a desired length of the billet is cured. That length can then be cut off the billet for use.
Conventionally, the billet is initially formed outside the input end of the press by manually stacking glue-bearing veneer sheets atop one another, one sheet at a time. Thus, the first sheet (whose lowermost, outward surface is non-glue-bearing) is manually laid on an assembly table and the first sheet's forward edge is manually aligned against a guide rail. The guide rail is then indexed upwardly and forwardly into a new position above the first sheet and a few inches forward of the first sheet's forward edge, while the first sheet is held in a fixed position. A second glue-bearing sheet is manually laid atop the first sheet and the second sheet's forward edge is manually aligned against the guide rail. The guide rail is then indexed upwardly and forwardly again, into a new position above the second sheet and a few inches forward of the second sheet's forward edge. The process is repeated until a billet having a desired number of plys has been assembled, with the forward and rearward ends of each sheet in the billet offset lengthwise with respect to the immediately adjacent sheet(s).
The prior art process described above is cumbersome and time consuming. The press' throughput is constrained by the time required to assemble the veneer sheets and incorporate them onto the end of the billet as it is fed into the press. The present invention overcomes these disadvantages by assembling a "packet" of veneer away from the press and delivering the assembled packet ready for incorporation onto the end of the billet being fed into the press.